I'd also second the Nemesis. You can kick it with any of the 3 batteries, and with the 18350 it's pretty small. You would need at least a spare battery, that's for sure. Depending on the wattage and usage it can last quite a bit actually. I took it out at 10 watts for a night and when I got back the battery was at 3.6V after 5 hours of regular usage, if I recall correctly the last time the Kick2 shut down the battery it was at 3.2V. However using the Nemesis in 350 mode without the kick is just so damn small, just a bit smaller than the size of an 18650 or about the size of a 15ml bottle.